Generally, the cantilever type caliper brake, as disclosed in Japanese Utility Model Publication Gazette No. 51-25,893, is constructed such that (1) a pair of brake arms each having a brake shoe is supported independently rotatably to a pair of fixing bases welded to a front fork or a rear fork at the bicycle frame, (2) between each fixing base and each brake arm is interposed a return spring for biasing the brake arms to enlarge the distance between the brake shoes, and (3) a hanging wire is provided across the idle ends of the brake arms, so that the hanging wire is pulled at the middle point thereof to swing the brake arms for exerting the braking action.
The center-pull type caliper brake is so constructed that one fixing base is fixed to a bridge provided across the front fork or the rear fork, a pair of brake arms is supported independently rotatably to the fixing base, return springs are provided at the brake arms respectively the same as in the above-described cantilever type caliper brake, and a hanging wire is provided to be pulled at the middle point thereof for exerting the braking action.
It is difficult to position the fixing bases of the above-described cantilever type caliper brake their at proper positions; as a result the bases may be vertically shifted from their proper positions. Also, it is very difficult to fix each fixing base such that its shaft axis is kept parallel to the plane perpendicular to the axis of the wheel rim of the bicycle; as a result, the shaft axis may be, e.g., tilted laterally of the perpendicular plane. As a result, each brake shoe is subject to being positioned inaccurately relative to the wheel rim, whereby a shoe clearance between the respective brake shoes and the wheel rim cannot be uniform, thereby creating a problem in that the braking effect is one-sided.
Separate return springs are used in the respective brake arms, whereby it is difficult to achieve a uniform spring force for each return spring because of manufacturing variations. As a result, each brake shoe is subject to being positioned inaccurately with respect to the wheel rim, thereby creating also a problem in that the braking effect is one-sided.
In addition, in the center-pull type caliper brake, the fixing base can force an altered mounting angle with respect to the bicycle frame to position each brake shoe inaccurately with respect to the wheel rim, or the return springs may not have a uniform spring force, whereby a uniform shoe clearance cannot be obtained.